1. Field
The present disclosure generally relates to the design of a hybrid optical source. More specifically, the present disclosure relates to the design of a hybrid optical source with optical proximity coupling between a semiconductor reflector and a grating coupler.
2. Related Art
Optical interconnects or links based on silicon photonics have the potential to alleviate inter-chip communication bottlenecks in high-performance computing systems that include multiple processor chips and memory chips. This is because, relative to electrical interconnects, optical interconnects offer significantly improved: bandwidth, density, power consumption, latency, and range.
In order to make a very low power (for example, less than 1 pJ/bit) optical interconnect, a high-efficiency optical source, such as a semiconductor laser or a laser source, is typically required. In particular, the required power consumption of the laser source may need to be 0.4 pJ/bit, and the required optical-waveguide-coupled wall-plug efficiency (defined as the laser power coupled into a silicon optical waveguide divided by the total consumed electrical power) of such a laser source usually needs to be greater than 10%. (While the energy cost of the laser source can, in principle, be better amortized at higher data rates, in practice receiver sensitivity decreases at higher data rates because there is less received photon energy per bit and the power consumption of receiver circuits using a given CMOS technology typically grows super-linearly with the data rate.) In addition, if silicon-photonic resonator devices (such as ring modulators) are used in an optical interconnect, the spectral linewidth of the laser source may need to be less than 10 pm.
However, most state-of-the-art laser sources have a wall-plug efficiency of only 1-2%. In these laser sources, a large amount (in excess of 80%) of the electrical power is usually consumed by thermal-electric cooling (TEC) to maintain high-power (greater than 10 mW) lasing with stable wavelength and good slope efficiency. While uncooled laser sources with sufficient wall-plug efficiency (around 10%) and output power (for example, 2-4 mW) are available for use in optical interconnects, the wavelength stability of these laser sources is often larger than 100 pm (because of the lack of temperature control), which is unsuitable for dense wavelength-division-multiplexing links. In addition, these laser sources are usually based on III-V semiconductors (such as indium phosphide, etc.). The large optical coupling loss between an optical waveguide in the III-V semiconductor laser source and a silicon optical waveguide could reduce the efficiency by 3-10 times.
Hence, what is needed is an optical source without the problems described above.